Proton NMR Imaging is rapidly becoming a major diagnostic tool in health care. The technique offers high resolution images without the use of ionizing radiation. Diagnostic capability can be enhanced with Contrast Agents, such as paramagnetic ions, provided they are site-directed and show low toxicity. Phospholipid Vesicles (liposomes) are small submicroscopic shell-like structures which can encapsulate and localize paramagnetic materials within certain tissues in the body. The aim of this work is to determine the extent to which entrapped paramagnetic ions alter proton relaxation rates (related to image contrast) for tissue known to have marked uptake of vesicles. Of particular interest, is evaluating certain vesicle formulations which have significant uptake by at least ten murine tumor types. In some instances, as much as 15% of the total injected dose of radiolabeled vesicle have accumulated in the tumor. If successful, the research offers a new opportunity for improving diagnostic specificity with NMR imaging. In addition to targeted or altered biodistribution, contrast agents in vesicles will very likely exhibit lower toxicity. These advantages coupled with the low risk to patients by NMR imaging represent a large and very useful commercial enterprise fulfilling a long standing need by radiologists.